1. Field
This disclosure relates to a vapor deposition reactor using plasma and a method for forming thin film using the same.
2. Description of the Related Art
During chemical vapor deposition (CVD) or atomic layer deposition (ALD), simultaneous application of precursors and plasma is often required. Plasma may be generated by applying voltage between two or more electrodes facing each other. FIG. 1 is a cross-sectional view of a conventional direct plasma type vapor deposition reactor. The direct plasma type vapor deposition reactor includes a chamber 106, a pair of electrodes 101, 102 located in the chamber 106 and spaced apart from each other, and a power source 103. By applying voltage between the pair of electrodes 101, 102 by means of the power source 103, plasma may be generated between the pair of electrodes 101, 102 and applied to a substrate 100. Further, a source precursor or a reactant precursor may be injected onto the substrate 100 through an injection hole 104 of the chamber 106. The source precursor or the reactant precursor may be discharged out of the chamber 106 through an exhaust hole 105.
By using the vapor deposition reactor as illustrated in FIG. 1, a thin film with relatively superior density characteristics may be obtained compared to the thin film produced by thermal decomposition. In addition, the vapor deposition reactor of FIG. 1 allows a low temperature process using plasma.
However, the substrate 100 may be damaged and decomposition by-products may be mixed into the thin film because the plasma is directly applied onto the substrate 100. For example, when a metal-organic source is used, a large quantity of carbon may be generated. Also, to generate capacitive type plasma, a low pressure or high vacuum is required. However, the plasma generated by a high voltage may result in the generation of particles or deterioration of the film property because of the generation of fine arc. Finally, when a pulse power is applied from the power source 103 for the purpose of ALD, the plasma may not be stabilized in short time, particles may be generated due to the repeated switching on and off of the plasma, which increases reflected power.
FIG. 2 is a cross-sectional view of a conventional remote plasma type vapor deposition reactor. The vapor deposition reactor of FIG. 2 includes a chamber 206, a first coil 201 and a second coil 202 located outside the chamber 206 and spaced apart from each other, and a power source 203. When using inductively couple plasma, the first coil 201 and the second coil 202 may be a single winding coil. When power is applied between the first coil 201 and the second coil 202 from the power source 203, plasma may be generated at a location distant from a substrate 200 and then applied to the substrate 200 as remote plasma. Further, a source precursor or a reactant precursor may be injected onto the substrate 200 through an injection hole 204 of the chamber 206.
With the remote plasma type vapor deposition reactor reduces the damage of the substrate 200 because the plasma is generated at a location distant from the substrate 200. In addition, the remote plasma enables a low temperature process. However, a thin film may not be formed uniformly across the center of the substrate 200 to its edge because the plasma is applied non-uniformly to the substrate 200. Further, the volume of the chamber 206 needs to be increased to uniformly inject the source precursor or the reactant precursor to the substrate 200, which results in increased consumption of the source precursor or the reactant precursor.
U.S. Pat. No. 6,435,428 discloses a showerhead type reactor equipped with a plasma generating apparatus. The reactor of this patent has a plasma generating electrode inside a showerhead. A source gas and a reactant gas excited by plasma are injected into a chamber so that thin film is formed by radical-assisted CVD or ALD. The reactor of U.S. Pat. No. 6,435,428, however, requires the use of an insulator such as ceramic for the showerhead in order to apply the plasma. In addition, the inside of the showerhead needs to be insulated for electrical isolation of the source gas and the reactant gas while requiring an electrode for generating plasma. Moreover, an O-ring has to be used to prevent leakage of gas between parts because the showerhead is assembled using ceramic parts that are not welded for insulation. This may result in deterioration of reliability and durability.
Further, with the reactor of U.S. Pat. No. 6,435,428, plasma can be generated only at the reactant gas because the source gas may be decomposed and deposited by the plasma. Accordingly, in order to prevent the effect of plasma when the source gas passes through a channel of the reactant gas, a gas injection tube made of insulating material such as ceramic or quartz is inserted in an upper plate above the electrode. In this case, if the materials of the showerhead and the gas injection tube have different thermal expansion coefficients or if there is a gap between the tubes, the source gas may flow into the channel for plasma generation and may be deposited inside the showerhead. The deposition around the tube may result in disconnection between electrodes when thin films made of metal or the like is to be formed, thereby making it impossible to generate plasma.